Milling system

ABSTRACT

A very high speed adiabatic face milling machine whose configuration and operation provide a highly efficient machining process suitable for production manufacturing conditions. The milling machine preferably operates at speeds of approximately 15,000 sfm and at efficiencies of approximately 7 cubic inches per minute per horsepower. The preferred milling operation is conducted without the use of cooling liquids, instead employing a chip removal system which enables the milling machine to operate truly adiabatically such that no heat is transferred to the workpiece or the cutter. The efficiency of the chip removal system is such that chip recutting is nearly eliminated and tool life is improved. The milling machine also includes an improved cutter structure, fixturing, and transfer devices.

This is a continuation of application Ser. No. 08/444,221, filed May 18,1995, abandoned, which is a division of application Ser. No. 07/875,231,filed Apr. 28, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally related to milling machines and theiruse in milling nonferrous metals, such as aluminum. More specifically,this invention relates to a face milling machine whose construction andoperating parameters provide for an adiabatic very high speed machiningprocess with improved tool life and operating efficiencies, wherein thechips are evacuated from the workpiece and the cutter without the use ofcooling liquids or lubricants. In addition, the milling machine includesaccessories that further promote the adiabatic operation, precision andefficiency of the milling operation.

2. Description of the Prior Art

Milling machines are widely used in manufacturing processes forproducing close tolerance parts, from flat surfaces to slots, keywaysand various complex contours. In particular, face milling machines areemployed where planar surfaces are to be machined to flatness tolerancesof 0.003 inches (0.076 millimeters) and less. Face milling machinestypically include a spindle which is rotatably held perpendicular to thesurface of a workpiece. The cutting element, or cutter, is generally adisc mounted to the end of the spindle. The cutter has a number of teethformed on, or alternatively, a number of cutting inserts mounted at, itsperimeter, such that the outside diameter of the cutter removes thestock from the workpiece being machined. The cutter is rotated by thespindle, which in turn is driven by a motor of suitable horsepower.Cooling liquids are commonly used to lubricate, cool and flush chipsfrom the workpiece and cutter. Finally, the workpiece and spindle aremoved relative to each other to feed the workpiece into the cutter,denoted as the feed rate and traditionally measured in inches perminute. Alternatively, feed rates are provided in inches per tooth,given by the formula:

    FR/((RPM)(t));

where FR is the feed rate (the rate of relative movement between theworkpiece and the spindle) in inches per minutes, RPM is the rotationalspeed of the spindle in revolutions per minute, and t is the number ofcutting teeth or inserts on the cutter.

Cutting speed, and its relation to feed rate, is of primary importanceif a milling machine is to efficiently produce close tolerance, highsurface quality parts. In the past 25 years, particular attention hasbeen concentrated on cutting speed and its effects on the quality andefficiency of the milling process. Cutting speeds are indicated insurface feet per minute (sfm) which can be calculated by the followingformula:

    2π(r)(RPM);

where r is the radial dimension of the cutting teeth from the spindle'saxis of rotation in feet, and RPM is the rotational speed of the spindlein revolutions per minute. Appropriate cutting speeds are dependent uponseveral factors--primarily the material being cut and the material ofthe teeth or cutting inserts used, with nonferrous metals, such asaluminum, and carbide cutting inserts usually allowing for higher cutterspeeds.

No one classification of cutting speeds has been generally accepted, butthe 16th Volume of the Metals Handbook (9th Edition) entitled"Machining" and published by the American Society of Metals, suggeststhat cutting speeds can be classified as follows. Conventional cuttingspeeds are below 2000 sfm for nonferrous metals, and often less than 500sfm for ferrous metals. Higher speeds of 2000 to 6000 sfm are deemedhigh speed machining, speeds of 6000 to 60,000 sfm are deemed very highspeed machining, and speeds greater than 60,000 sfm are ultrahigh speedmachining. Obviously, one advantage to higher machining speeds is fastermachining time and thus higher production rates. A significantadditional benefit to high speed machining is that, past a criticalcutting speed which is characteristic of the particular material beingmachined, cutting forces actually decrease with increased spindle speeduntil a minimum is reached, which is again a characteristic of the givenworkpiece material. Accordingly, cutting forces at higher speeds canactually be comparable to or less than that at conventional speeds. Lowcutting forces are not only desirable from the standpoint of the powerrequirement of the spindle's motor, but are particularly desirable whenmachining very thin, nonrigid workpieces.

Finally, an additional benefit to high speed machining is the ability toachieve a substantially adiabatic cutting operation in which nearly allof the heat generated during the machining process is transferred to thchips formed, thus keeping the cutter and the workpiece essentially attheir original pre-machining temperatures. In addition to being able tohandle the workpieces immediately after machining, other significantadvantages to achieving an adiabatic operation are improved cuttingefficiency, less spindle power, lower noise levels, higher precisioncuts, less workpiece deflection, and improved tool life. Again, suchadvantages are particularly beneficial when machining thin, nonrigidworkpieces.

Moreover, a coolant is not always needed under adiabatic machiningconditions, and in fact may adversely serve to transfer heat from thechips back to the workpiece and cutter. Though cooling liquids generallyimprove tool life and the appearance of the machined surface, theyrequire extensive delivery, filtering and often cooling systems. Also,the use and disposal of cooling liquids are a growing health andenvironmental concern. Accordingly, dry machining provides severalsignificant advantages over the use of coolants.

However, to sustain a truly adiabatic cutting operation, particularattention must be given to the type of material being cut and thematerial of the teeth or cutting insert, the appropriate feed, speed anddepth of cut, the precision by which the spindle is supported relativeto the workpiece, the stiffness of the cutter, and the ability of thefixturing to rigidly and accurately support the workpiece.

To date, practically all scientific investigation in the area of highspeed adiabatic machining of aluminum has been limited to small endmills (0.5 to 1 inch in diameter) at speeds from approximately 10,000 toapproximately 60,000 rpm--or roughly 2600 to 15,700 sfm. In practice,such high rotational speeds are severely limited by bearing size, withsmaller bearings allowing higher rotational speeds. However, smallerbearings simultaneously limit spindle power and stiffness, resulting incutting speed being inversely proportional to power and stiffness.Consequently, cutting forces and horsepower limitations have effectivelyconstrained testing to much lower speeds--typically, below 5000 sfm--forpurposes of developing milling machines which are practical for use inproduction manufacturing. Simultaneously, stiffness of the spindle andthe manner in which the cutter is mounted to the spindle has alsolimited cutter size, significantly limiting material removal rates.

In terms of cutting efficiency or unit power (cubic inches per minuteper horsepower), the industry has generally concluded from testing thusfar that, though cutting forces and specific power are reduced at higherspeeds, these advantages tend to diminish above speeds of 5000 sfm.Maximum unit power for machining aluminum is generally believed to beapproximately 3 and as much as 4 cubic inches per minute per horsepowerat about 5000 sfm, with horsepower available from current motortechnology being limited to approximately 30 horsepower at these highspindle speeds. Accordingly, to achieve higher material removal rates inexcess of 40 cubic inches per minute generally requires higher-torquedrive motors which result in lower cutting speeds, defeating theadvantages of high speed cutting.

Moreover, cutting tool manufacturers do no recommend using cuttingspeeds in excess of 3000 sfm for aluminum cutting with diamond underrealistic production manufacturing conditions, though a few recognizespeeds as high as 12,000 sfm as being viable. However, such higherspeeds have generally been limited to carbide and diamond cutting tools.Diamond cutting tools, such as polycrystalline diamond (PCD)-tippedcarbides, have recently become popular for cutting aluminum because ofimproved tool life--by a factor of 10 to 100 over tungsten carbidecutting tools. However, diamond cutting tools are relatively brittle andare therefore limited by the ability of the milling machine's stiffnessand workpiece stability to avoid impact loads caused by workpiece andcutter vibration, particularly at higher cutting speeds. Accordingly,diamond tool manufacturers currently recommend maximum cutting speeds of1500 to 2500 sfm.

From the above discussion, it can be readily appreciated that the priorart testing does not suggest or support advantages to machining aluminumat speeds in excess of 5000 sfm. Generally, the limitations of highspeed milling include spindle stiffness, excessive horsepowerrequirements, and cutting tool limitations, spindle/cutting toolinterface limitations, and machine feed rate capability. Accordingly,high speed milling has not been widely employed under typicalmanufacturing conditions, even where there is a need to surface machinethin workpieces. As a result, the industry conventionally has turned togrinding for such applications. However, even where the abovelimitations have been achieved under strict laboratory test conditions,the prior art has failed to achieve high material removal rates,particularly in terms of specific power (i.e. cubic inches per minuteper horsepower).

Accordingly, what is needed is a cost-efficient adiabatic millingmachine capable of operating without cooling liquids at very highspeeds, while affording improved tool life and material removal ratesand surface finish, and which is particularly adapted to precisionmilling thin aluminum workpieces in production manufacturing.

SUMMARY OF THE INVENTION

According to the present invention there is provided an adiabatic veryhigh speed face adiabatic milling machine whose configuration andoperation provide a highly efficient machining process suitable forproduction volume manufacturing conditions. The milling machinepreferably operates at speeds of approximately 15,000 sfm and atefficiencies of approximately 7 cubic inches per minute perhorsepower--a factor of 2 greater than that known in the prior art.Moreover, the preferred milling operation is conducted without the useof cooling liquids, instead employing a chip removal system whichenables the milling machine to operate truly adiabatically such that noheat is transferred to the workpiece or the cutter. The efficiency ofthe chip removal system is such that, unexpectedly, tool life is nearlydouble that which would be expected otherwise.

In particular, the milling machine of the preferred embodiment includestwin-spindles which move in unison on opposite sides of a base structureto allow for simultaneous machining and repositioning passes relative totwo identical groups of workpieces being machined. In addition, themilling machine employs a cutter, spindle, fixturing and transferdevices which are all adapted to contribute to the adiabatic operation,precision and efficiency of the milling process. Having the aboveattributes, the milling machine of the present invention is able toadiabatically machine and repeatedly produce finished precisionworkpieces under high volume production manufacturing conditions whereflatness and parallelism tolerances are 0.001 inch (0.025 millimeters)or less.

Each spindle is mounted to the base structure so as to be rotatably heldnearly perpendicular to the surface of a workpiece. In addition, thebase or a portion thereof is slidable in a longitudinal direction of themachine to reciprocate the spindles in unison relative to theirrespective workpieces at speeds of approximately 550 to 600 inches perminute. The cutters are each a large diameter disc mounted to the end ofeach spindle with a number of irregularly-spaced diamond cutting insertsmounted near the cutter's perimeter. To prevent cutting at the radiallyinward "heel" of the inserts, a cam adjustment feature is includedbetween each spindle and the base such that the toe of the spindles canbe readily adjusted to present only the radially outward cutting edge ofeach insert to the workpiece. In addition, each spindle can be finelyadjusted to account for different toe requirements between roughing andfinishing cuts. Due to added stiffness being induced by the manner inwhich each cutter is mounted to its spindle, the cutters are capable ofbeing rotated by their respective spindles at high speeds without lossof precision in the cut or damage to the diamond cutting inserts atspeeds which otherwise exceed levels recommended by the industry.Moreover, the large diameter of the cutters used permit cutting speedsto be readily attained in the range of 10,000 to 20,000 sfm to achievean adiabatic machining operation. Finally, the large diameter of thecutters permits very high surface speeds without resorting to highrotational speeds, thereby avoiding the aforementioned limitationsresulting from attempts at optimizing bearing size.

Due to the large diameter of the cutter and the high speeds at which itrotates, material removal rates in excess of 7 cubic inches per minuteper horsepower are achievable. The large quantity of chips formed duringthe adiabatic machining operation are eliminated from the area of thecutter and workpiece through the chip removal system. The chip removalsystem includes a pressure source which generates a pressuredifferential between an enclosure that peripherally surrounds the cutterand fixturing that both supports and closely surrounds the workpiece.Clearances between the enclosure and fixturing and between the fixturingand the workpiece, provide sufficiently high speed air flow from theambient surroundings to completely envelope the workpiece. Preferably,the air speed corresponds to the speed of the chips as they leave thecutter to augment the manner by which they are evacuated. As a result,the air flow serves to efficiency and substantially evacuate all thechips from the immediate machining area, preventing heat transfer fromthe chips back to the workpiece and cutter. Moreover, efficient removalof the chips from the cutting area also prevents recutting of the chips,which would otherwise significantly reduce tool life as well as theoverall efficiency of the process.

In addition to having significantly higher rigidity in relation to itsmass, the cutter is also specially adapted to assist in excluding chipsfrom between the cutter and workpiece. The cutter is disc-shaped havingpockets in its peripheral surface to receive the cutting inserts andgullets which are specifically formed to assist in the elimination ofthe chips. The cutting inserts are preferably diamond-tipped carbideswhich perform well at high temperatures and are not prone to gallingwith nonferrous materials, thereby enhancing the adiabatic capabilitiesof the milling machine.

The milling machine includes fixturing which also utilizes techniquesthat induce added rigidity in the workpieces, while reliably clampingand damping each workpiece to enable machining to within small flatnesstolerances. Finally, transfer devices are employed to accurately andsecurely locate the workpieces within the fixture and transfer theworkpieces between subsequent stages of the milling machine to enableprecision machining of both sides of the workpiece. Each of the abovecan be programmably controlled to optimize their operation while alsominimizing the amount of manpower necessary to operate the millingmachine.

According to a preferred aspect of this invention, the cutting speed isspecially selected to enhance the adiabatic operation of the millingmachine at a high workpiece feed rate through the cutter. The speed andfeed of the milling machine are most suited to the machining ofnonferrous materials, and more specifically cast aluminum and magnesiumalloys. The combination of a very high cutting speed and high feed ratereduces unit power requirements on the order of two times thatpreviously recognized by the prior art. In addition, the lower cuttingforces associated with the lower unit power requirements allow for facemilling of thin, nonrigid workpieces, such as automotive transmissionvalve bodies. Consequently, the milling machine of the present inventionis also well suited for machining flat surfaces having numerous surfaceinterruptions therein.

In addition, the manner in which the chips are handled after machiningfurther complements the milling machine's adiabatic operation. The chipremoval system precludes chips from fouling the workpiece or cutter soas to prevent heat transfer back to the cutter or workpiece. Efficientelimination of the chips from the cutting area also serves to improvetool life. The preferred operation of the milling machine is dry--i.e.without cooling liquids or lubricants. Accordingly, ad added benefit isthat the chips can be easily recycled without the need to separate thechips from a liquid in an expensive discrete chip removal system.Moreover, the absence of cooling liquid and lubricant vapors as well aswaste allows the machining operation to be conducted in a moreenvironmentally advantageous manner.

Another significant advantage of the present invention is that the useof a large diameter cutter enables the milling machine to operate atvery high surface speeds while the added static and torsional rigidityof the cutter promotes accuracy and precision of the cut using diamondcutting inserts. The structure of the cutter enables the cutter toassist in eliminating the chips from the cutting area while alsopreventing chips from accumulating between the cutter and workpiece. Inaddition, the orientation of the spindle can be quickly adjusted toensure that the toe of the cutter is appropriate for the type andcondition of cut desired, i.e. roughing or finishing. The cutter canalso be adjusted to minimize radial runout for achieving improvedsurface finish. Accordingly, the orientation and construction of thecutter and spindle is adapted to promote a fully adiabatic machiningoperation.

Finally, the manner in which the workpieces are fixtured relative to thecutter enables precision machining of thin nonrigid workpieces. Also,the manner in which the workpieces are transferred into and out of thefixturing device promotes precision positioning and machining of theworkpieces under high volume production manufacturing conditions.

Accordingly, it is an object of the present invention to provide a facemilling machine whose operation is adiabatic and whose cutting speed andfeed rate provide material removal rates with lower cutting forces andunit power requirements superior to that of the prior art.

It is a further object of the invention that the milling machine includea dry chip removal system which substantially prevents heat transferfrom the chips to the cutter or workpiece so as to enhance the adiabaticmachining process.

It is still a further object of the invention that the dry chip removalsystem include a device for creating a pressure differential between anenclosure surrounding the cutter and the workpiece with the ambientsurroundings, wherein the enclosure includes a shroud circumscribing thecutter and as mask having an opening therethrough sized to closely fitthe contour of the workpiece so as to create accelerated air flow andcreate an air curtain effect.

It is another object of the invention that the milling machine include adisc-shaped cutter which is specifically structured to assist in theremoval of chips from the cutting environment and to preclude chips fromcollecting between the cutter and the workpiece.

It is yet another object of the invention that the cutter have enhancedrigidity for precision operation at high cutting speeds.

It is still another object of the invention that the milling machineinclude a spindle whose orientation to the workpiece is finelyadjustable to accommodate both roughing and finishing cuts as well asadjustment for runout tolerances.

It is an additional object of the invention that the milling machineinclude fixturing which can securely position and damp a workpieceduring machining while also inducing added rigidity into thin workpiecesand thin portions of workpieces to withstand cutting forces withoutvibration and obtain satisfactory machined workpieces within requiredtolerances.

It is yet an additional object of the invention that the milling machineinclude transfer devices which can secure the workpieces duringtransporting of the workpieces to the fixture, while also promotingaccurate and secure placement of the workpieces for fixturing andmachining.

Other objects and advantages of this invention will be more apparentafter a reading of the following detailed description taken inconjunction with the drawings provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a face milling machine in accordancewith the preferred embodiment of this invention;

FIG. 2 is a front view of the face milling machine of FIG. 1;

FIG. 3 is a side view of the face milling machine of FIG. 1;

FIG. 4 is a cross-sectional view of the milling machine taken along line4--4 of FIG. 3;

FIG. 5 is a front view of a transfer arm for use with the millingmachine of FIG. 1;

FIG. 6 is a cross-sectional view of the transfer arm taken along line6--6 of FIG. 5;

FIG. 7 is a cross-sectional view of the spindle and cutter of the facemilling machine taken along line 7--7 of FIG. 3 in accordance with thepreferred embodiment of this invention;

FIG. 7A is a cross-sectional detail view of the cutter body and adapterof FIG. 7 exaggerating the faces and raised portions between the adapterand cutter;

FIG. 8 is a top view of the cutter taken along line 8--8 of FIG. 7;

FIG. 9 is a detailed front view of the cutter in accordance with apreferred embodiment of this invention;

FIG. 10 is a top view of a transfer bar of the milling machine of FIG.1;

FIG. 11 is a front view of the transfer bar in accordance with apreferred embodiment of this invention;

FIG. 12 is a cross-sectional view of the transfer bar taken along line12--12 of FIG. 10 in accordance with the preferred embodiment of thisinvention;

FIG. 13 is a top view of a fixture of the milling machine of FIG. 1 inaccordance with a preferred embodiment of this invention;

FIG. 14 is a cross-sectional view of the fixture taken along line 14--14of FIG. 13;

FIG. 15 is a side view of the spindle taken along line 15--15 of FIG. 2and illustrating its mounting face; and

FIG. 16 is a cross-sectional view of the spindle mounting face takenalong line 16--16 of FIG. 15 in accordance with a preferred embodimentof this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Machine Configuration

With reference to FIGS. 1 through 4, there is shown a dual-spindle facemilling machine 10 in which a pair of spindles 12a and 12b are mountedon opposite sides of a base 14. The base 14 is equipped with a strokingdevice (not shown), such as a motor driven ball screw known in the art,which strokes the spindles 12a and 12b in unison in a fore and aftdirection. The spindles 12a and 12b are also movable in a verticaldirection by any suitable method, such as a motor driven ball screw 15which strokes both the spindles 12a and 12b and a portion of the base 14to which the spindles 12a and 12b are attached.

Each spindle 12a and 12b is independently powered by a variable speedmotor 16a and 16b of a type known to the art. In the preferredembodiment, each motor 16a and 16b is capable of producing 30 horsepowerand speeds of approximately 5000 rpm. However, it is preferable that themotors 16a and 16b draw current only to sustain the rotational speed ofthe spindles 12. Accordingly, only one motor 16a and 16b drawssufficient current to machine at any given time--i.e. each motor 16a and16b draws sufficient current to maintain its rotational speed as aworkpiece 20 is being machined by its corresponding spindle 12a or 12b,permitting the spindles 12a and 12b to be synchronized to alternatebetween machining and repositioning operations. As an example, while thefirst spindle 12a is driven by its motor 16a to perform a machiningoperation on a workpiece 20, the other spindle 12b also moves in thesame direction, but practically coasts under its own inertia as it isbeing repositioned for its next machining pass.

Each spindle 12a and 12b is provided with a workpiece support structure18a and 18b upon which the workpieces 20 are supported and transportedin sequential fashion to and from a pair of cutting units 22a and 22bcorresponding to the pair of spindles 12a and 12b. In the preferredembodiment, the workpieces 20 are transported on each side of themilling machine 10 in groups of three to increase efficiency of onespindle 12 during machining while minimizing the time needed toreposition the other spindle 12. In addition, there is a transfer arm 24located between the workpiece support structures 18a and 18b fortransferring the groups of three workpieces 20 therebetween. After thefirst cutting unit 22a machines a group of workpieces 20 on a first oftwo sides of each workpiece 20, the transfer arm 24 rotates theworkpieces 20 180 degrees as they are transferred to the next workpiecesupport structure 18b so as to expose a second side of each workpiece 20to the second cutting unit 22b.

Consequently, the path of a workpiece 20 is U-shaped around the millingmachine 10. One set of workpieces 20 is first transported along thefirst workpiece support structure 18a to the first cutting unit 22a(i.e. down the upper half of the first leg of the U) and secured by afirst set of fixtures 28a (to be described more fully below) to undergoa first machining pass of the first side of the workpieces 20.Simultaneously, a second group of workpieces 20 are being machined atthe second cutting unit 22b (on the second leg of the U). During themachining pass of the first spindle 12a (either in a fore or aftdirection), the second spindle 12b is moved in the same direction as thefirst spindle 12a for repositioning so as to be ready for its nextmachining pass. Subsequently, after the first group of workpieces 20 aremachined by the first spindle 12a, they will be further transported downthe first workpiece support structure 18a, rotated by the transfer arm24 over to the second workpiece support structure 18b (i.e. along thebase of the U), and transported upon the second workpiece supportstructure 18b (i.e. up the power half of the second leg of the U) towarda second set of fixture 28b where it is again secured to be machined bythe second cutting until 22b. While the second spindle 12b is machiningthe workpiece 20, the first spindle 12a is being repositioned to machinethe next workpiece 20 (both being stroked in a direction opposite thefirst spindle's 12a machining pass and the second spindle's 12brepositioning pass). Throughout the above process, power is beingdirected to either spindle 12a or 12b, whichever is machining aworkpiece 20, while the remaining spindle 12a or 12b is allowed toalmost free wheel, thus conserving power consumption of the millingmachine 10. Following the above process, machining of both sides of aworkpiece 20 is accomplished. In the preferred embodiment, whereseparate rough and finish passes are required, two milling machines 10would be located adjacent each other, with a first milling machine 10being used to perform a roughing cut, while the second performs asubsequent finishing cut on the same workpieces 20.

Transfer Bar

As illustrated in FIGS. 1, and 10 through 12, the workpiece supportstructures 18a and 18b each slidably support transfer bars 26a and 26b,respectively, by which the workpieces 20 are transferred to and from thecutting units 22a and 22b. Essentially, the transfer bars 26a and 26bare a pair of beams 120 which are spaced apart a distance less than thelength of the workpieces 20 so as to be able to support the workpieces20 lengthwise. Each beam 120 has a height substantially greater than itswidth. The lengths of the beams 120 are roughly half the length of theworkpiece support structures 18a and 18b to allow reciprocation of thetransfer bars 26 along the length thereof by a suitable stroking device122 (see FIG. 4) mounted to the workpiece support structure 18. Thetransfer bars 26a and 26b are each stroked between a loading station124a and 124b and an unloading station 148a and 148b beneath theirrespective cutting units 22a and 22b.

As best seen in FIG. 10, for each workpiece 20 there is a pair oflocking arms 130 attached to the upper edge of each beam 120 at its endcorresponding to its loading station 124. The locking arms 130 are eachoriented to have its length substantially parallel to its correspondingbeam 120. The locking arms 130 are positioned on the beams 120 to locatefour corners 128 of the outer periphery of each workpiece 20. Thelocking arms 130 are each pivotably attached to its respective beam 120with a pivot pin 140 between an abutment end 132 and a camming end 134of the locking arm 130. The camming end 134 includes a slot 136 formedin the locking arm 130 which limits the pivoting movement of the lockingarm 130 by camming against a pin 138 extending upwardly from the beam120. Also mounted at the camming end 134 is a spring 142 or othersuitable biasing device which biases the camming end 134 outward fromthe beam 120 so as to bias the abutment end 132 inward toward acorresponding corner 128 of the workpiece 20. As shown, each corner 128on the workpiece 20 is preferably an arcuate slot sized to fit acorresponding radial contour of the abutment end 132.

Located at each loading station 124a and 124b on the outward side ofeach beam 120 are a pair of vertical columns 126 corresponding to eachpair of locking arms 130. The columns 126 are located relative to theircorresponding beam 120 so as to correspond to the location of theircorresponding pair of locking arms 130 when the transfer bars 26 arepositioned at the loading station 124 by the stroking device 122. Thecolumns 126 each include a lateral arm 144 which extends sufficientlyinward to cam against the camming end 134 of a corresponding one of thelocking arms 130 when the beams 120 are at the loading station 124. Thelateral arms 144 force the camming end 134 of each locking arm 130inward, which forces the abutment end 132 outward to disengage thecorner 128 of the workpiece 20 while the transfer bars 26 remain at theloading station 124.

In operation, a set of workpieces 20 are first loaded onto a platform 34by any suitable lifting device (not shown). The transfer bars 26 arethen raised by a lifting device 121 at the loading station 124 to liftthe workpieces 20 from the platform 34. The transfer bars 26 thenslidably move along the workpiece support structure 18 in the directionof the cutting unit 22. As the transfer bars 26 leave the loadingstation 124, the lateral arms 144 disengage their corresponding cammingends 134 of the locking arms 130, allowing the abutment ends 132 of eachlocking arm 130 to engage its corresponding corner 128 of a workpiece20, thereby frictionally locking each workpiece 20 in place on thetransfer bars 26. Once positioned below the cutting unit 22, theworkpiece support structure 18 and the transfer bars 26 are both loweredover a fixture 28 (as hereinafter disclosed) by the suitable liftingdevice to forcibly disengage the workpiece 20 from the locking arms 130and engage the workpiece 20 with the fixture 28. Thereafter, while theworkpiece support structure 18 is still in the lowered position, thetransfer bars 26 are moved back to the loading station 124 to pick upthe next set of workpieces 20.

Transfer Arm

Once the machining operation is complete at the cutting unit 22, theworkpieces 20 are again lifted off the fixture 28 by a rear portion 146of the transfer bars 26 at the end of the transfer bars 26 opposite thelocking arms 130. The workpieces 20 are then moved to the unloadingstation 148 of the workpiece support structure 18, where they aregrasped by the transfer arm 24. The transfer arm 24, as illustrated inFIGS. 5 and 6, includes a suitable base structure 150 from which thetransfer arm 24 rotates between the first workpiece support structure18a and the second workpiece support structure 18b. The primary functionof the transfer arm 24 includes rotating the workpieces 20 so that amachining operation can be performed on their opposite surfaces.However, it is necessary that the workpieces 20 be precisely picked andplaced from one side of the milling machine 10 to the other so that thetransfer bars 26b corresponding to the workpiece support structure 18bcan grasp the workpieces 20 with their corresponding locking arms 130.

To achieve this feature, the transfer arm 24 includes a parallel pair ofgrasping arms 152a and 152b corresponding to each workpiece 20 to betransferred. The grasping arms 152 extend parallel to each other fromthe end of the transfer arm 24, as can be seen in FIG. 6. Each adjacentpair of grasping arms 152 is spaced apart to form a slot 170 whose widthis sufficient to receive the width of the workpiece 20. The graspingarms 152 each include at least one clamping arm 154. In the preferredembodiment, a first grasping arm 152a has one clamping arm 154a whilethe second grasping arm 152b has two spaced-apart clamping arms 154b and154c as shown. As a result, the workpiece 20 is grasped at three pointswhich stabilizes the workpiece 20 as it is transferred between theworkpiece support structures 18a and 18b.

Each clamping arm 154 is pivotably secured within a cavity 168 in itsgrasping arm 152 by a pivot pin 156. Each clamping arm 154 has anengagement end 158 and a stroking end 160 on opposite sides of the pivotpin 156. Accordingly, the engagement end 158 is able to retract into itscavity 168 during repositioning of the transfer arm 24, and extend intothe slot 170 between the grasping arms 152 to engage the workpiece 20. Atorsion spring 164 biases the clamping arm 154 into the slot 170 toengage the workpiece 20, while a suitable stroking device 166, such as ahydraulic or pneumatic cylinder, is provided to force the clamping arm154 to retract into the cavity 168 and thus disengage the workpiece 20.The travel of the clamping arm 154 into the slot 170 is limited by astop 162 formed in the cavity 168 adjacent the stroking end 160 of theclamping arm 154.

In the operation of the transfer arm 24, the workpieces 20 aretransported by the transfer bars 26 to the transfer arm 24 aftermachining. The transfer bars 26 align the workpieces 20 relative totheir respective grasping arms 152 such that each workpiece 20 will nestwithin a corresponding slot 170 once the transfer arm 24 is moved intoposition. The transfer arm 24 is then rotated upon its base 150 toengage the workpieces 20. With the grasping arms 152 on either side of aworkpiece 20, the clamping arm 154a of the first grasping arm 152a isallowed to rotate into the slot 170. The stop 162 sufficiently limitsthe rotation of the clamping arm 154a such that the clamping arm 154a isprevented from sharply impacting the workpiece 20, which would otherwisemisalign the workpiece 20 relative to the transfer arm 24 andsubsequently the transfer bars 26b of the second workpiece supportstructure 18b. As such, the clamping arm 154a serves as a datum pointfor locating the workpiece 20 relative to the transfer arm 24, thesecond grasping arm 152b and the transfer bars 26b. Thereafter, thesecond and third clamping arms 154b and 154c are allowed to rotate intothe slot 170 and clamp the workpiece 20 against the first clamping arm154a. The torsion springs 164 provide sufficient biasing to secure eachworkpiece 20 as it is rotated by the transfer arm 24 into position forthe second pair of transfer bars 26b. Once in place on the second pairof transfer bars 26b, the process is repeated, beginning with thetransport of the workpieces 20 to the second cutting unit 22b.

While the preceding description has specifically recited a dual-spindlearrangement for purposes of the preferred embodiment, it will be clearto those skilled in the art that the very high speed adiabatic operationof the milling machine 10, to be described below, is not dependent uponsuch limited structure. Accordingly, the teachings of the presentinvention outlined below are not limited to the above describedstructure or operation.

Spindle

As noted above, the face milling machine 10 of the present inventionincludes the spindles 12 which are mounted to the base 14. As best seenin FIG. 7, the spindles 12 each include a housing 30 within which thespindles 12 are rotatably supported above their corresponding fixture28. Mounted at the lower end of each spindle 12 is one of theaforementioned cutting units 22. The cutting units 22 are generallyoriented perpendicular to the axis of rotation of the spindle 12 andsubstantially parallel to the fixtured workpieces 20.

With reference now to FIGS. 15 and 16, each housing 30 includes amounting surface 60 which abuts the portion of the base 14 which isintended to move vertically with the spindle 12 during its operation. Anumber of holes 68 are formed along the perimeter of the mountingsurface 60 through which slightly undersized bolts 70 can secure thespindle 12 to the base 14. Formed in the upper half of the mountingsurface 60 on a vertical line of symmetry is an aperture 62 in which ahardened journal 64 is installed. The journal 64 is sized to receive ashaft 66 extending from the base 14, by which the housing 30 issupported by the base 14. The journal 64 and shaft 66 allow pivotalmovement between the spindle 12 and the base 14 when the bolts 70 aresufficiently loosened.

Located on the perimeter of the mounting surface 60 is an opening 72which serves as a camming surface for an eccentric shaft 74 rotatablyextending from the base 14. Attached perpendicularly from the eccentricshaft 74 is a lever 76 by which the eccentric shaft 74 can be rotated.The lever 76 can be either operated by hand or by any suitable device,such as the hydraulic cylinder 75 shown. By rotating the eccentric shaft74, its camming effect against the opening 72 causes the housing 30 tocontrollably pivot about the shaft 66. The radial spacing of the opening72 from the journal 64 enables the spindle 12 to be angularly adjustedrelative to a workpiece 20. Accordingly, sufficient toe of the cuttingunit 22, i.e. the degree by which the cutting unit's plane of rotationdiffers from the plane of the workpiece 20, can be provided to avoidimpacting the trailing edge of the cutting unit 22 against theworkpieces 20 or otherwise creating cross-hatching in the machinedsurface, both of which result in drastically reduced tool life. The toecan also be selectively altered to adapt to a particular cuttingoperation, such as a roughing operation or a finishing operation. In thepreferred embodiment, the toe for a roughing cut is approximately 0.0025inches, while the toe for a finishing cut is approximately 0.0005inches. These settings can be readily obtained by operation of theeccentric shaft 74 within the opening 72.

Moreover, by automating the adjustment of the spindle 12 with a devicesuch as the cylinder 75, the spindle 12 can be pivoted to machine in twodirections. As an example of an alternate embodiment employing thismethod, the spindle 12 can be oriented to provide a 0.0025 inch toewhile the workpiece 20 is fed through the cutting unit 22 in onedirection to perform a roughing cut; thereafter, the spindle 12 can bepivoted by the eccentric shaft 74 to provide a 0.0005 inch toe in theopposite direction to perform a finishing cut on the workpiece 20. Suchan arrangement can, in certain applications, eliminate the need for twoseparate milling machines 10 which are each dedicated to either aroughing or finishing operation, by providing the capability forbi-directional cutting.

With further reference to FIG. 7, each spindle 12 is supported bybearings 32 whose preloads ensure that the spindle 12 is sufficientlysupported for operating at speeds up to approximately 4000 rpm. Eachspindle 12 is driven through a coupling 36 by its respective motor 16.The lower end of each spindle 12 extends outside of its housing 30,terminating in the cutting unit 22. Each cutting unit 22 includes anannular-shaped adapter 38 or drive member, a mounting device 40, and acutter 42. The adapter 38 is mounted directly to the spindle 12 by anumber of bolts 41, while the cutter 42 is mounted to the adapter 38with the mounting device 40. The mounting device 40 preferably employs aball-locking feature (not shown) which reduces the effort needed tooperate the mounting device 40. Such a mounting device 40 is disclosedin U.S. Pat. Nos. 3,498,653 and 4,135,418.

There are two further advantages to the use of this type of mountingdevice 40 over the conventional method of using mounting bolts andkeying the cutter 42 to the spindle 12. Firstly, such a mounting device40 provides accurate axial mounting of the cutter 42 relative to thespindle 12. Secondly, the mounting device 40 provides infinite radialindexing of the cutter 42 relative to the adapter 38. Such indexingenables the total axial runout at the cutter 42 relative to theworkpiece 20 to be reduced by matching the high axial runout region onthe adapter 38 with the low axial runout region of the cutter 42. Bydoing so, the effect is for the axial runout regions to cancel eachother to some degree, thereby reducing waviness in the workpieces'sfinished surface. Waviness of less than 0.0005 inch has been achievedusing this method. Not only is this a significant advantage in terms ofsurface quality, but the effect is to improve tool life because wavinessin the finished surface is usually the criterion applied to decide whento replace the cutter's inserts.

Cutter

As can be seen in FIGS. 7 and 8, the cutter 42 is substantiallydisc-shaped. The cutter 42 includes a number of cutting inserts 54mounted within a like number of pockets 56 formed on the cutter'sperimeter 43. The preferred diameter defined by the placement of theinserts 54 on the cutter is approximately 20 inches. Accordingly, with arotational speed of 2800 rpm, the surface speed of the inserts 54 is14,660 sfm. The solid disc shape of the cutter 42 is contrary to priorart cutters, which are typically annular shaped to provide clearancebetween the cutter and a workpiece, to reduce weight, and to improveease of handling. However, with the teachings of the present invention,the solid disc shape of the cutter 42 forms a planar lower surface 46which clears the workpiece 20 by approximately 0.030 inches duringmachining. This minimal clearance prevents chips from accumulating in arecess of the cutter 42 which would otherwise create an imbalance andvibration in the cutter 42, while also serving to prevent the workpiece20 from breaking free of its fixture 28 if a clamping anomaly occurs.The solid disc shape also provides added inertial mass which encouragesthe cutter 42 and spindle 12 to coast during repositioning.

In addition to the lower surface 46, the cutter 42 is defined by thecylindrical perimeter 43, an upper surface 48 and a central opening 44.The mounting device 40 is mounted in the central opening 44 so as to beflush with the lower surface 46 of the cutter 42. The mounting device 40abuts a radially extending should 55 in the opening 44, so as to drawthe cutter 42 against the adapter 38 when the mounting device 40 isengaged with the adapter 38 and tightened. The upper surface 48 of thecutter 42 includes a central raised surface 50 circumscribing theopening 44, and a annular raised surface 52 at its perimeter 43. Theannular raised surface 52 is preferably elevated approximately 0.002inches above the central raised surface 50, as best illustrated in FIG.7A, in which the height difference between the central raised surface 50and the annular raised surface 52 is exaggerated.

Accordingly, with the mounting device 40 tightened, the annular raisedsurface 52 contacts the outer perimeter of the adapter 38 first.Thereafter, further tightening of the mounting device 40 causes thecutter 42 to distort until the central raised surface 50 also abuts theadapter 38. Consequently, the lower surface 46 of the cutter 42 isconcave by approximately 0.002 inches. By distorting the cutter 42 inthis manner, significant added stiffness is induced into the cutter 42relative to its mass, permitting high speed machining of flat surfaceswith significant surface interruptions, such as channels formed inautomotive transmission channel plates. In addition, the annular raisedsurface 52 serves as a frictional drive surface for the cutter 42, withno significant torsional loads being imposed on the mounting device 40during operation of the cutter 42.

The manner in which the cutter 42 is mounted to the adapter 38 offers anadded capability of adapting the cutter 42 to produce a roughing andfinishing cut within the same pass of a workpiece 20. However, thediameter of the cutter 42 must be sufficient for the workpiece 20 to fitwithin the diameter defined by the inserts 54. In addition, the inserts54 must be provided with both an outer and inner radial cutting edge. Asan example, the outer radial cutting edge may be adapted for roughingwhile the inner radial cutting edge is adapted for finishing. In astress-free state, the cutter 42 would orient the attitude of theinserts 54 to present the inner radial cutting edges to the workpiece20. Finally, the mounting device 40 must be adapted to be adjustablewhile the cutter 42 is rotating.

Applying this method, the cutter 42 is deflected by the mounting device40 a predetermined axial distance relative to the adapter 38 prior toencountering the workpiece 20. The axial distance is chosen to bothdeflect the cutter 42 sufficiently to induce rigidity and alter theattitude of the inserts 54 such that they present their outer radialcutting edges to the workpiece 20 for roughing. Once the leading edge ofthe cutter 42 has machined the workpiece 20 and the workpiece 20 iscentrally positioned beneath the cutter 42 and not subject to machiningby any of the inserts 54, the mounting device 40 is adjusted to decreasethe deflection in the cutter 42 while maintaining sufficient rigidity inthe cutter 42. However, the change in deflection in the cutter 42 issufficient to reverse the attitude of the inserts 54 such that theypresent their inner radial cutting edges to the workpiece 20 forfinishing. As a result, one single pass of the cutter 42 is capable ofboth roughing and finishing the workpiece 20.

This capability may also be desirable in combination with the rotatablespindle 12 to provide further capability of effectively altering theinsert geometry or clearances to thereby effect the characteristics ofthe finished surface.

As best seen in FIG. 8, the inserts 54 are irregularly spaced about theperimeter 43 of the cutter 42 in a nonrepeating fashion to substantiallyproduce "white noise" during the operation of the cutter 42, therebyavoiding the inducement of vibration at a single frequency. In addition,the inserts 54 are recessed into their respective pockets 56 apredetermined depth toward the cutter's center. The depth to which eachinsert 54 is positioned is inversely proportional to the distancebetween the insert 54 and the insert 54 which precedes it during themachining operation. As a result, the additional material which would beremoved from the workpiece 20 due to an insert's greater spacing fromits preceding insert 54 is compensated for by recessing the insert 54 toreduce its depth of cut into the workpiece 20. Accordingly, chip load issubstantially uniform, promoting more uniform tool wear and longer toollife. In addition, more uniform torsional loads result as each insert 54successively engages the workpiece 20.

As shown in FIG. 9, adjacent each insert 54 is a gullet 58 formed on theperimeter 43 of the cutter 42. Conventionally, gullets 58 provide alimited void adjacent an insert 54 into which chips can escape as theyleave the insert 54. In contrast, according to the present invention thegullets 58 extend completely across the full width of the cutter 42 andguide the chips in an upward direction away from the workpiece 20. Asviewed from the side of the cutter 42, the circumferential width of eachgullet 58 increases toward the upper surface 48 of the cutter 42. Asviewed from above, illustrated in FIG. 8, the radial depth of eachgullet 58 also increases toward the upper surface 48 of the cutter 42.Accordingly, as the cutter 42 is rotated at high rotational speeds, backpressure downstream of the gullet 58 is prevented. Moreover, a pressuredifferential is believed to be created between the upper surface 48 andthe lower surface 46 of the cutter 42, further encouraging the chips totravel away from the workpiece 20 and toward the upper surface 48 of thecutter 42.

Inserts

With further reference to FIG. 9, the inserts 54 are preferably a squaretungsten carbide body with a polycrystalline diamond (PCD)/tungstencarbide wafer brazed in a recess on one corner of the tungsten carbidebody. Such construction is generally known in the art. The inserts 54are also slightly wedge-shaped for purposes of increasing the clampingforce upon the insert 54 when acted upon by centrifugal forces whilerotating at high speeds.

As is also known in the art, diamond cutting tool materials arepreferable for machining aluminum and its alloys due to their hightemperature capability and their low tendency for bonding, or galling,with the aluminum during machining, as would be typical with tool steelsand carbides. Traditionally, the tool industry has not recommendeddiamond cutting materials for cutting speeds greater than 2500 sfm dueto their brittleness. However, the superior rigidity of the cutter 42 inconjunction with the ability to precisely set the toe of the cutter 42with the spindle 12 enables the milling machine 10 of the presentinvention to utilize diamond inserts where the prior art has failed toachieve adequate insert life.

As illustrated for a finishing cut, the diamond inserts 54 have positiveradial and axial rake angles of 5 degrees. In contrast, the diamondinserts 54 preferably have a negative radial and axial rake angle ofapproximately 5 degrees for roughing cuts. In addition, the cornerradius of the inserts 54 is dependent upon the type of cut made.Preferably, an insert for a roughing cut has a radius of 0.060 inchwhile an insert for a finishing cut has a radius of 0.005 inch. Theclearance angle of the inserts 54 for both types of cuts is preferably14 degrees.

As noted above, the spacing of the inserts 54 is nonrepeating. Toevaluate surface finish capability of a given insert geometry and alsoascertain tool life relative to an insert's placement on the perimeter43 of the cutter 42, testing is currently underway under manufacturingconditions in which each insert 54 is serialized with its correspondingpocket 56. The performance of each serialized insert 54 is thenmonitored by assessing the workpiece surface finish produced andtracking the number of workpieces machined with a given set of inserts54. When the inserts 54 are removed, the condition of each insert 54 isthen evaluated. Knowing the location of each insert 54 on the cutter 42permits a statistical analysis of the surface finish of the part,including any tendency to produce waviness in the parts. To date 140,000pieces per insert set have been achieved, with even greater tool lifebeing anticipated with further modifications being suggested by presentresults.

Adiabatic Process

In combination, the above elements--including cutting speed, feed rate,cutting insert material and spindle and cutter construction--enable themilling machine 10 of the present invention to achieve a true adiabaticshearing operation of aluminum alloy workpieces 20 during chipformation. In the art of machining, adiabatic chip formation has beenknown to be attainable at sufficiently high surface speeds. However,surface speed rates which are practical for use in productionmanufacturing operations have been a significant limitation in the priorart, in part due to the inability to provide a spindle whose bearingswill allow high rotation speeds while also providing sufficientrigidity. As a practical matter, surface speeds of greater than 5000 sfmhave not been recognized as improving efficiency by the prior art whenmachining aluminum. In addition, the prior art has provided cutterswhich have limited rigidity for viable use of surface speeds of greaterthan 10,000 sfm. Insufficient rigidity of a cutter is incompatible withthe brittle nature of a diamond cutting tool, whose use is preferabledue to superior tool life and its ability to avoid galling withaluminum. Moreover, material removal rats greater than 4 cubic inchesper minute per horsepower have generally been unattainable, therebydemanding excessive horsepower requirement at high surface speeds usinglarge diameter cutters.

According to the present invention, an adiabatic process is achieved atspeeds between 10,000 and 20,000 sfm, with optimal results beingattained at speeds of approximately 14,660 sfm. With a diameter of 20inches for the cutter 42 of the present invention, the required rotationspeed of the cutter is approximately 2800 rpm. As noted above, the addedrigidity of the cutter 42 due to its deflection as mounted to theadapter 38 is sufficient to overcome the shortcomings of the prior artattributable to insufficient rigidity for machining at these elevatedspeeds. In addition, lower cutting forces are also achieved at thepreferred cutting speed, making the process particularly suited formachining very thin aluminum workpieces 20.

In conjunction with this preferred speed, the workpieces 20 are machinedat feed rates of about 600 inches per minute, and more preferably at arate of approximately 580 inches per minute (and specifically, 0.008inches per tooth), as provided by the spindle 12 as it is propelled byits stroking device. Without the use of a liquid coolant and understandard manufacturing conditions the above parameters have provided atrue adiabatic machining process in which both the workpieces 20, thecutter 42 and the inserts 54 exhibit no detectable temperature riseafter being completely machined. Unexpectedly, the above parameters havealso permitted efficiencies in excess of 7 cubic inches per minute perhorsepower.

As a result, the milling machine of the present invention operates atefficiencies much greater than that known in the prior art. As anexample, under actual manufacturing conditions aluminum has beenmachined at the rate of 720 cubic inches per minute. The machiningoperation of the present invention has also provided low cutting forceswith the added advantage or preventing the formation of burrs andbreakouts in the workpiece 20, a not uncommon occurrence when machiningsurfaces having irregular or intricate surface features. Moreover,surface flatness of less and 0.001 inch has been readily attainablewithout thermal distortion from high cutting temperatures. Tool life inexcess of 130,000 workpieces has also been attained with the abovedescribed adiabatic machining operation of the milling machine 10 of thepresent invention.

Vacuum Shroud and Deck

Once a chip is severed from the workpiece 20 with all of the heatgenerated being absorbed in the chip, it is imperative to evacuate thechip from the area of the cutter 42 and the workpiece 20 to prevent heattransfer thereto. The importance of this aspect is compounded by thehigh material removal rate possible with the milling machine 10 of thepresent invention. Accordingly, to ensure that the chips are quicklyevacuated, the milling machine 10 incorporates a chip removal systemwhich includes a device for creating a pressure differential between thecutting environment, including a surrounding structure 90 enclosing thecutter 42, and the ambient surroundings. In the preferred embodiment,this device is a large capacity vacuum system (not shown) capable ofcreating a flow rate of approximately 3500 cubic feet per minute.However, the primary parameter has been determined to be the velocity ofthe air flow, which is preferably closely matched with the surface speedof the cutter 42, i.e. 14,660 feet per minute. The surrounding structureor enclosure 90 determines the air speed past the workpiece 20 andcutter 42 in conjunction with the air capacity of the vacuum system.

As best seen in FIG. 14, the surrounding structure 90 includes a shroud78 and a mask 80. The shroud 78 is mounted to the spindle 12 while themask 80 is supported by a lifting mechanism 102 which transports themask 80 between a lower machining position and an upper position. Theupper position permits the transfer bars 26 to bring the workpieces 20into position beneath the mask 80 while the mask 80 and itscorresponding spindle 12 are both raised and the spindle is beingrepositioned for the next machining pass. The lifting mechanism 102 canbe of any suitable design, such as a limited stroke hydraulic cylinder.

The shroud 78 circumscribes the cutter 42 to form a peripheral enclosurethereto, while the mask 80 has an opening 92 which closely follows thecontour of the workpiece 20. Together, the mask 80 and the workpiece 20form the lower surface of the surrounding structure 90. The air flowthrough the surrounding structure 90 enters between the shroud 78 andthe mask 80, and between the mask 80 and the workpiece 20, as will bedescribed in greater detail below. Along with the suspended chips, theair flow leaves the surrounding structure 90 through a duct 88, which inturn is routed to a suitable receiving container (not shown) or thelike. To reduce the necessary capacity of the vacuum system, computercontrolled dampers (not shown) are preferably installed in each duct 88near the shroud 78 to provide air flow in the surrounding structure 90only during a machining pass by that cutter 42.

As best seen in FIG. 1, the shroud 78 has an elongated portion 81extending in the direction of the spindle's travel relative to theworkpiece 20 to better prevent chips from escaping if a large concaveportion is encountered in a workpiece 20. Referring again to FIG. 14,the shroud 78 has an upper and lower converging wall 82 and 84,respectively, and an intermediate wall 86. The lower converging wall 84is disposed to be adjacent the mask 80, so as to form a predeterminedclearance therebetween. The lower converging wall 84 also serves todeflect chips vertically upward into the air stream as they leave thecutter 42, thus improving the efficiency of the chip removal system. Theupper converging wall 82 further serves to deflect the chips into theair flow as they enter the duct 88.

As noted above, the opening 92 in the mask 80 is sized to closely fitthe contour of the workpiece 20, creating a second predeterminedclearance. As will be described in greater detail below, a speciallyadapted fixture 28 is provided to ensure that the workpieces 20 are ableto withstand the significant peripheral air movement and the pressuredifferential between their upper and lower surfaces. Moreover, as asafety feature the minimal 0.030 inch clearance between the lowersurface 46 of the cutter 42 and the workpieces 20 also serves to preventthe workpieces 20 from becoming completely disengaged from their fixture28. The combination of the predetermined clearances between the shroud78 and the mask 80, and the mask 80 and the workpiece 20 determine theair speed given a flow capacity provided by the vacuum system. Bysufficiently limiting the clearances, speeds of at least 14,000 feet perminute are achieved, corresponding to the surface speed of the cutter42, and thus the speed of the chips as they leave the workpiece 20.

In addition, the air flow between the mask 80 and the workpiece 20creates a peripheral air curtain that aids in deflecting errant chipsback into the surrounding structure 90. As a result, no furtherenclosure of the milling machine 10 is necessary to contain the chipsand protect bystanders. Accordingly, the surrounding structure 90defined by the shroud 78 and the mask 80 is substantially smaller thanenclosures typically employed in the prior art.

Fixtures

As noted above, the fixture 28 which holds the workpieces 20 isspecially adapted to withstand the loading of the workpieces 20 as theybecome subjected to the vacuum of the chip removal system. Moreimportantly, the fixture 28 is specifically adapted to firmly secureextremely thin aluminum workpieces 20 in a manner that enables thecutter 42 to produce surfaces within a flatness tolerance of within0.002 inch. As seen in FIGS. 13 and 14, each fixture 28 consists of atleast three primary rests 94, one or more secondary rests 95, athree-jaw chuck 96, a two-jaw chuck 98, and a number of damping devices100.

Generally, the primary rests 94 serve to support the workpieces 20within the opening 92 of the mask 80 and at a predetermined verticalposition relative to the cutter 42. The primary rests 94 are preferablyspaced apart relative to one another or as the workpiece 20 designprovides to ensure that a stable three-point platform is provided foreach workpiece 20.

The three-jaw chuck 96 is a hydraulic or pneumatically-actuated deviceof the type well known in the art. The three-jaw chuck 96 has three jaws97 whose composite outer perimeter is sized to engage a cavity or firstaperture 108 in the workpiece 20 so as to securely clamp the workpiece30 on the fixture 28 in the plane of the mask 80. As an added feature,the outer peripheral surface of each jaw 97 has a lower of chromenodules 106 deposited thereon to a thickness of approximately 0.020 bywhich the workpiece 20 can be better gripped. The chrome nodules 106 canbe deposited by any known method, such as electroplating. Attached toone of the jaws 97 so as to extend above each jaw 97 is a debris cover101 to prevent ships from becoming trapped between the jaws 97.

The two-jaw chuck 98 is essentially a standard hydraulic orpneumatically-actuated chuck having two jaws 110 which are angularlyspaced approximately 180 degrees apart from each other. With thisarrangement, the two-jaw chuck 98 is adapted to engage a cavity orsecond aperture 112 in the workpiece 20 in a manner that, upon the jaws110 engaging the aperture 112, the portion of the workpiece 20 betweenthe apertures 108 and 112 is deflected slightly downward into thefixture 28. This externally induced deflection in the workpiece 20causes rigidity in the workpiece 20, enabling the workpiece 20 to betterwithstand the cutting forces associated with the milling operation.

Similar to the three-jaw chuck 96, the two-jaw chuck 98 also includes adebris cover 101 and has a layer of chrome nodules 106 deposited to theouter periphery of each jaw 110 by which the workpiece 20 can be bettergripped. In addition, the two-jaw chuck 98 includes an accelerometer 99to detect vibration in the fixture 28. If the vibration exceeds apredetermined level, the output of the accelerometer 99 can be used toshut down the milling machine 10 to allow the fixture 28 to becorrected, and thereby avoid damage to the milling machine 10 andpersonnel.

The downward direction in which the workpiece 20 is deflected isdetermined by the fact that the missing jaw would be the jaw furthestfrom the three-jaw chuck 96. As such, the two jaws 110 engage the sideof the second aperture 112 nearest the first aperture 108 so as tocompress the upper surface of the workpiece 20, forcing the lowersurface of the workpiece 20 downward. The extend to which the workpiece20 is deflected is determined by the second rests 95, which arepositioned a predetermined distance below the plane of the primary rests94. In the preferred embodiment, the second rests 95 are threaded postswhich can be shimmed to accurately adjust the amount of deflection inthe workpiece 20. Logic dictates that the predetermined distance must beless than the flatness tolerance of the workpiece 20, and morepreferably the minimum amount necessary to achieve the desired effect.

The damping devices 100 are strategically positioned about the peripheryof the workpiece 20 immediately below the mask 80 to damp vibrations inthe workpiece 20 and selectively deflect specific portions of theworkpiece 20 either toward or away from the cutter 42. The dampingdevices 100 each include a hydraulically or pneumatically actuated lever114 which is pivotably mounted to a base 116. The lever 114 is orientedto be substantially vertical, having an upper engagement end upon whichis deposited a layer of chrome nodules 106 for gripping the workpiece 20in the same manner as the two- and three-jaw chucks 98 and 96.

The damping devices 100 can be positioned relative to the workpiece 20such that the lever 114 engages the workpiece 20 either as the upperengagement end is rotating upward toward a vertical position or rotatingdownward from a vertical position. Under the former condition, theassociated edge of the workpiece 20 will be deflected upward toward thecutter 42. Under the latter, the associated edge of the workpiece 20will be deflected downward away from the cutter 42. Under eithercircumstance, added rigidity will be induced into the workpiece 20 tobetter withstand the cutting forces associated with the millingoperation. In addition, the damping devices 100 can be positioned suchthat their cumulative effect is to urge the workpiece 20 against anabutment block (not shown), so as to provide another feature whichserves to secure the workpiece 20.

In operation, the transfer bars 26 lower the workpieces 20 onto thefixture 28 while the mask 80 and spindle 12 are lifted out of the way.Because the workpieces 20 are frictionally held on the transfer bars 26by the locking arms 130, the fixture 28 forcibly strips the workpieces20 from the transfer bars 26, assuring that the workpieces 20 properlynext within the fixture 28 against the primary rests 94. Thereafter, thethree-jaw chuck 96 engages its corresponding aperture 108, followed bythe two-jaw chuck 98 which engages its corresponding aperture 112. Thedamping devices 100 then move in to abut the periphery of the workpiece20. Together, the two-jaw chuck 98 and the damping devices 100 cooperateto selectively deflect the workpiece 20 in a manner that inducesrigidity without distorting the surface of the workpiece 20 outside ofthe desired flatness tolerance.

A significant advantage of the milling machine 10 of the presentinvention is that the cutting speed is specially selected to enhance theadiabatic operation of the milling machine 10 at a high workpiece feedrate through the cutter 42. The speed and feed of the milling machine 10are most suited to the machining of nonferrous materials, and morespecifically aluminum alloys. The construction of the milling machine 10also permits extremely high efficiencies of approximately 7 cubic inchesper minute per horsepower--a factor of two greater than that known inthe prior art. In addition, the lower cutting forces associated with thevery high cutting speeds allow for face milling of thin, nonrigidworkpieces 20, such as transmission channel plates. Consequently, themilling machine 10 of the present invention is also well suited formachining flat surfaces having complex surface patterns with significantsurface interruptions, such as channels formed in automotivetransmission channel plates.

In addition, the manner in which the chips are handled after machiningfurther complements the milling machine's adiabatic operation. The chipremoval system precludes chips from folding the workpieces 20 and cutter42 so as to prevent heat transfer thereto. The preferred operation ofthe milling machine 10 is dry--i.e. without cooling liquids orlubricants. Accordingly, an added benefit is that the chips can beeasily recycled without the need to separate the chips from a liquid.Another advantage to dry machining is that the machining operation canbe conducted in a more environmentally sound manner.

Another significant advantage of the present invention is that thecutters 42 are attached to their respective spindles 12 in a mannerwhich supplements their rigidity, thus allowing the use of diamondcutting inserts 54 for machining aluminum at very high speeds. Thecutters 42 are also formed to discourage chips from accumulating betweenthe cutters 42 and workpieces 20. In addition, the orientation of thespindles 12 can be readily adjusted with the eccentric shaft 74 toensure that the toe of each cutter 42 is appropriate for tolerancevariations and for the type of cut desired, i.e. roughing or finishing.Accordingly, the orientation and construction of the cutter and spindleare adapted to promote a fully adiabatic machining operation.

Finally, the manner in which the workpieces 20 are fixtured relative tothe cutter 42 and transferred into and out of the fixture 28 promotesprecision and secure positioning and machining of the workpieces 20under high volume manufacturing conditions. The fixtures 28 are able todeflect each workpiece 20 sufficiently to induce added rigidity into theworkpiece 20 while remaining within the tolerance requirement for thesurface of the workpiece 20. The fixtures 28, transfer bars 26 andtransfer arms 24 are particularly adapted to be regulated by a suitablecontroller which would ensure synchronized cooperation between eachdevice.

In contrast to prior art laboratory testing, the advantages of themilling machine 10 can be realized within a typical manufacturingenvironment at a combination of surface speeds, fed rates, rigidity andpower which were previously unviable for such purposes. The millingmachine 10 of the present invention has overcome previous bearinglimitations by increasing the diameter of the cutter 42 to reduce thenecessary spindle speed. The cutter 42 of the present invention ispermitted to have a large diameter due to its solid construction and theadded rigidity induced by the manner in which the mounting device 40 isable to adjustable clamp the cutter 42 to the adapter 38. The addedrigidity of the cutter 42 also permits the use of diamond cuttinginserts 54, which would otherwise have low tool life due to vibration.Tool life and uniform chip load are also promoted by locating theinserts 54 in a nonrepeating fashion on the perimeter 43 of the cutter42 while simultaneously compensating for their irregular spacing byaltering the radial position of each insert 54. Finally, the uniquemanner in which the chip removal system is able to completely evacuatethe chips from the area of the cutter 42 and workpieces 20 enables themilling machine 10 to sustain the extremely high material removal ratewhich results from the very high machining surface speed. The cutter 42is provided with gullets 58 which also assist in evacuating the chipsfrom within the surrounding structure 90 surrounding the cutter 42 andworkpiece 20. The chip removal system of the present invention alsoprovides for superior tool life in excess of 130,000 workpieces forcutter set by preventing the recutting of chips. Each of the abovefeatures cooperate to provide an adiabatic face milling machine 10 whichis practical for modern manufacturing conditions.

While the invention has been described in terms of a preferredembodiment, it is apparent that other forms could be adopted by oneskilled in the art. Accordingly, the scope of the invention is to belimited only by the following claims.

What is claimed is:
 1. The fixturing device for supporting a workpieceduring a machining operation, said fixturing device comprising:means forsupporting said workpiece on at least three points; means adjacent saidsupport means for engaging at least one edge of said workpiece, saidengaging means deflecting at least a portion of said workpiece in adirection towards said support means; and secondary means for supportingsaid workpiece located adjacent said engaging means, said secondarysupport means having an elevation which is a predetermined distancebelow a plane defined by said at least three points, said secondarysupport means limiting the deflection of said workpiece to saidpredetermined distance; whereby added rigidity is induced in saidworkpiece as a result of deflecting said workpiece said predetermineddistance.
 2. The fixturing device of claim 1 further comprising anabutment member adjacent said support means, wherein said engaging meanscreates a resultant force which urges said workpiece against saidabutment member.
 3. The fixturing device of claim 1 wherein saidengaging means comprises a plurality of damping devices.
 4. Thefixturing device of claim 3 wherein said plurality of damping deviceseach comprise an engagement surface having a coarse chrome layerdeposited thereon.
 5. A fixturing device for supporting a workpiecehaving an aperture therein, said workpiece having at least one generallyplanar surface and having at least one edge extending generallytransverse to said surface during a machining operation, said fixturingdevice comprising:means for supporting said workpiece; and means forinducing a force in said workpiece, said force inducement means beingspaced a predetermined distance from said support means, said forceinducement means engaging said at least one edge of said workpiece anddeflecting at least a portion of said surface of said workpiece apredetermined distance toward said fixturing device whereby engagementof said at least one edge of said workpiece by said force inducementmeans deflects at least a portion of said surface of said workpiece apredetermined distance such that added rigidity is induced in saidworkpiece as a result of said deflection of said at least a portion ofsaid workpiece.
 6. The fixturing device of claim 5 wherein said supportmeans comprises at least three support members.
 7. The fixturing deviceof claim 5 wherein said predetermined distance is less than apredetermined tolerance of said workpiece.
 8. The fixturing device ofclaim 5 further comprising at least one abutment member located adjacentsaid support means, wherein said force inducement means creates aresultant force which urges said workpiece against said at least oneabutment member.
 9. The fixture device as claimed in claim 5 whereinsaid force inducement means further comprises a plurality of dampingdevices located about the periphery of said workpiece, each of saidplurality of damping devices having an engagement surface for engagingthe peripheral edge of said workpiece such that engagement of saidengagement surface of each of said plurality of damping devices deflectsat least a portion of said workpiece a predetermined distance towardssaid fixturing device such that added rigidity is induced in saidworkpiece as a result of said deflecting of said workpiece.